Check-in and check-out block signaling system using regular track circuits



N.- D. PRESTON 2,895,043

ING SYSTEM July 14, 1959 CHECK-IN AND CHECK-OUT BLOCK SIGNAL USING REGULAR TRACK CIRCUITS Flled March 20; 1957 INVENTOR. ND. PRESTQN HIS ATTORNEY 6 n m? 2m ii En EN m5 Sm EN m5, 5 5 E Q n NP i 2,895,043 eHECK-IN also CHECK-OUT BLOCK s'IGN'AnnsIG SYSTEM USING REGULAR TRACK CIRCUITS Neil D. Preston, Rochester, N.Y., assignor to General Railway Signal Company, Rochester, N.Y.

Application March 20, 1957, Serial No. 647,248

3 Claims. (Cl. 246-41) United States Patent track relay connected across the rails at one end of the track section with a source of direct current energy and a limiting resistor connected across the track rails at the other end of the section. Normally, the track relay is energized; but when a train enters the track section and shunts the relay, the current in the track relay is reduced to a low value causing it to drop away. When the train leaves the track section, the track relay picks up again.

A block signaling system employing the above described organization is wholly dependent upon a continually effective train shunt. Beginning with the advent of lightweight train equipment such as Budd cars, which are now used quite extensively along with the conventional equipment, it has been experienced that such lightweight equipment does not always provide an adequate train shunt of the magnitude required to assure that the usual track relay, when once dropped away, will remain so. It has, however, also been experienced that such lightweight equipment does provide an adequate train shunt at intermittent intervals during its passage over a particular section of track, such shunt usually of sufiicient magnitude to cause the initial release of a track relay upon entrance of a train into a section.

An additional consideration arises out of the increased use of dynamic braking, excessive sanding, and other pertinent factors all of which contribute to the failure of the signaling system to respond merely because of the inability of the usual track cincuit organization to provide adequate detection.

Hence, it is one object of the present invention to pro vide a block signaling system of the nature described herein which provides complete protection against uncertain and erratic shunting action of any type train equipment.

Another 'object of the present invention is to provide a block signaling system which is adaptable to the usual track circuit organization with relatively few additional elements required, the addition of which will result in effective signaling for both lightweight and conventional train equipment.

A further object of the present invention is to provide a train check-in check-out arrangement adaptable to the usual track circuit organization which arrangement provides complete protection of the signaling system in that it requires restoration to be dependent upon the movement of the car out of the signaling block, as distinctive from a loss of shunt while such car is still physically present in the block.

A still further object of the present invention is to provide a block signaling system having its signaling circuit organization arranged so as to automatically test ice the safe performance of the track circuit by requiring each car or train as it passes into a block, to drop a track relay within a limited restoration time in order to clear a stop signal behind. This means provides repeated testing of shunting performances of each track circuit under the actual existing conditions of train shunt resistance, ballast resistance and other variable conditions.

Generally speaking, and without attempting to define the exact nature of the invention at this time, it is proposed to provide a system of train check-in check-out applied to a line circuit controlled by two or more track relays.

Such control permits a line relay to be deenergized by opening a stick circuit when the train enters the block, and prepares a pick-up circuit for the line relay when a train exits from the block. Since, in this disclosure, the signals are shown as being controlled by the line relays in accordance with the movements of trains through the blocks, deenergization of the line relay between a single shunting action will put the signal behind the train to stop, the system being arranged so that subsequent temporary or even permanent losses of shunt while the train is still occupying the block will not clear the signal.

Other objects, purposes and characteristic features of the present invention will in part be obvious from the accompanying drawing and will in part be more specifically described hereinafter. In describing the invention in detail, reference will be made to the accompanying drawing in which like reference characters designate corresponding parts throughout the system.

The single figure of drawing illustrates a stretch of track signalled for trafiic in one direction with the features of the present invention embodied therein.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawing having been made more with the purpose of making it easy to understand the principles and mode of operation than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts, sources of energy and other devices have been illustrated in a conventional symbolic manner.

Although the drawing indicates one specific arrangement for a particular system of block signaling, such drawing should not be considered as limiting the multiple variations available therefrom such as, providing all track sections with identical equipment in lieu of altering the organization for intermediate track sections as shown in the illustration.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries, or other sources of direct current; and the circuits with which these symbols are used, always have current flowing in the same direction. The symbols (B-}-) and (B) indicate connections to the opposite terminals of a suitable battery, or other direct current source which has a central or intermediate tap designated (C); and the circuits with which these symbols are used, may have current flowing in one direction or the other depending upon the particular terminal used in combination with the intermediate tap (C). In this particular case, certain of these symbols (B+), (B) and (C) are used in connection with line circuits in which the polarized line has been shown, but the common line has not been shown but is to be assumed as a part of the designated connection to (C).

Referring now to the drawing, a stretch of track having rails 3 is shown as having a plurality of track sections naling in accordance 'with the present invention.

organization shown at the exit end of section T2 and the I entrance end of section T3 may, however, be duplicated any number of times or, conversely, may be eliminated entirely, depending upon the number of track sections required for the length of the stretch of track being signalled. Thus the sections employing this latter organization are assumed to be typical of the various track sections found in a relatively long stretch of track. a

The stretch of track shown illustrates the use of three aspect signals which have been designated as signals 2 and 4. It should be noted that there are two insulated track sections between the signals 2 and 4. The signals are shown as being of the color light type; but it should be understood that any other suitable type of signal may be employed, if desired, such, for example, as searchlight signals. The respective lamps for these sig nals have been shown adjacent their circuits rather than carrying their circuits to the symbols themselves for the purpose of simplifying the drawing. The difierent signal lamps, designated as R, Y and G for identifying the different aspects of red, yellow and green of each signal, are shown as selected by a suitable home-distant relay HD associated with that signal.

In adapting the present invention to the usual track circuit organization, no change is necessary in the existing track circuits. The only adjustment of the existing track circuit needed is to make each track circuit responsive to shunting by a lightweight equipment at least once upon such lightweight equipment moving into and out of each block.

The supposition that the present invention is adaptable to the usual track circuit organization without change is predicated on the proposition that the existing direct current track circuits have sufiicient shunting sensitivity to respond to a shunting effect of lightweight equipment that is bound to occur at least now and then during its progress through the blocks. Track circuits not satisfying this condition,as will be pointed out more in detail later on, are identified by signals held at stop. If revision or adjustment cannot take care of these faulty track circuits, of course a primary-secondary relay combination or other expedient to improve the shunting sensitivity may be employed.

Considering therefore for purposes of illustration that the usual track circuit organization does have such above described shunting sensitivity, it will be noted from the drawing that each track section is provided with a track relay TR which has been given a distinctive preceding numeral corresponding to the track section with which it is used. For example, the track section T2 is provided with a track relay 2TR. These track relays are preferably connected to the track rails at the entrance end of the section, while at the exit end of the section a track battery TB is connected in series with a limiting resistor LR across the track rails.

Associated with the entrance end of each block is a home-distant line relay HD each of which has also been given a distinctive preceding numeral corresponding to the track section with which it is used, much in the same manner as pointed out above in connection with the discussion of the track relays.

These home-distant line relays HD are controlled over suitable polarized line circuits which includes contacts of all the track relays of the associated sections between signals. The polarized line circuit used in this disclosure also includes two external series resistance R1 and R2, both of which may be conveniently located adjacent'the exit-end of each block. The electrical characteristics of the line circuit are chosen so that the hornedistant line relay HD will operate the one of the two resistances in the circuit, but not both. Ordinarily, the substitution of a line relay of lower resistance than the kind normally used with the typical line battery, in addition to the insertion of the external resistances R1 and R2, will give the line circuit these desired operating characteristics. In this connection then, the home-distant line relay HD is released by completely opening its circuit, so that the inclusion of one or two external resistances in the circuit merely has to distinguish between current values which either pick up or release the line relay HD. 7

It should be pointed out with regard to each of the external series resistances R1 and R2 that both resistances can be shunted out of the line circuit by appropriate shunting circuits as shown on the drawing and in a manner to be discussed in further detail later'on. For the time being, however, suffice it to say that the shunting circuit for the external resistance R1 actually includes a front contact of the home-distant line relay HD, which,

while not a true stick circuit arrrangement, has the "or this external resistance R1 added to the presence of the external resistance R2 prevents any subsequent reene'rgization of the line relay HD if the particular track relay is again picked up by temporary or even a permanent loss of shunt.

The home-distant line relay of the type disclosed herein in the polarized linecircuit arrangement, must of course, be a retained neutral polar relay, or its equivalent, so it will not lock itself down upon a reversal of polarity in changing the signal indication from caution to clear.

Associated with the exit end of each block is a suitable approach relay SR, sometimes called a series track relay. These approach relays SR may be of any suitable type, but for convenience they have been shown as being connected in multiple with the limiting resistor LR for the corresponding track section. It should be pointed out that in the event a trackrelay of a center fed section is available, such track relay could just as well he used in place of any of the SR relays.

Also associated with the exit end of each block and the adjacent entrance end of the next block in advance is a restoration circuit which includes a slow acting repeater type restoration relay RC. Since complete protection in such a train check-in check-out arrangement requires that restoration be dependent upon the movement of the ear out of the section, as distinctive from 'a loss of shunt while the car is still physically present in a section, the initial energizing circuit of the restoration relay RC includes a front contact of the home-distant line relay HD of the block ahead. This prevents conditioning for restoration from occurring with another train operating a'head, otherwise conditions would be set up for a premature false restoration upon loss of shunt of the following car.

.While this arrangement provides and assures safe restoration, even in the case of a loss of shunt when approaching an occupied block, if the following car approaching an occupied block does not wait for the block to become unoccupied and the signal to clear, but instead passes the stop signal, there can be no restoration and a signal locked at stop is left behind. Although the next train passing through the blocks will right this condition, it will be stopped unnecessarily in doing so. Hence, an emergency push button EPB has been provided so that the engineer of a train passing a permissive stop signal may operate the emergency push button EPB and artificially energize the associated restoration relay RC.

It is believed that the nature of the invention, its advantages and characteristic features can be best understood with further description being set forth from the standpoint of operation.

The block signaling system shown by the drawing is of the normally energized type with the signals indicating clear when the blocks are unoccupied thus displaying a green signal aspect G. It is further assumed that all track relays TR are normally energized when the track section is unoccupied. For example, track relay 2R is energized over the track rails from track battery 2TB in series with the limiting resistor ZLR. The limiting resistor ZLR is provided to give a potential drop in the interrail potential when a train enters the track section T2, and also to prevent excessive current flow from the battery 2TB while the section is thus occupied.

Because all of the track relays are energized, all of the home-distant line. relays I-ID are also energized. More specifically, a home-distant line relay ZHD is energized from (13+) through a line circuit including front contact 36 of relay ll-ID, an external series resistance R2, front contact 51 of track relay 3TR, front contact 43 of track relay 2TR, front contact 32 of relay ZHD, windings of relay 2HD, to the micltap of the battery over common return wire (C). With the relay ZHD picked up by current of positive polarity, which as described above is the normal condition when the signal blocks are unoccupied, the polar contact 34 of relay 2HD is in its right-hand position thereby completing a circuit from through front contact 33 of relay ZHD, polar contact 34 of relay ZHD in its right-hand position, lamp G, to Thus, signal 2 is normally illuminated to display a green aspect.

Since, as stated before, each block has a similar organization and the track relays are always energized in their normal condition, the other signals such as signal 4 of corresponding blocks, normally display a green signal aspect. It should be understood, however, that one skilled in the art could adapt means whereby such signaling system is altered so as to be of the approach signaling type, as for example, adding a slow acting repeater relay (not shown) associated wtih the relay SR, a contact of which repeater relay could control the source of energy for the signal circuits.

Associated with the line circuit in each block is a shunting circuit used to momentarily shunt the external resistance R2 from the line circuit to permit ample energizing current to pass over the line circuit to pick up the home-distant line relay HD. Control of this shunting circuit is dependent upon the response of the restoration relay RC since the shuntingcircuit must be completed during the release time of the restoration relay RC, otherwise the combination of the external series resistances RI. and R2 will prevent sufficient energizing current to flow through the line relay I-ID to cause it to pick up.

Assuming that a train has entered onto the track section T2 and has been efiective at some time during its presence to shunt the track relay 2TR and thus drop front contact 43 of the track relay 2TR, the dropping away of contact 43 interrupts the line circuit 2A and deenergizes the line relay ZHD. With the line relay ZHD in its deenergized condition, front contacts 32 and 33 respectively of relay ZHD drop away. Opening of contact 32 interrupts the circuit by which the external resistance R1 was shunted from the line circuit and renders the resistance R1 effective. The dropping away of front contact 33 interrupts the supply circuit for energizing the lamp G and the subsequent closing of back contact 33 of relay ZHD completes a circuit for the red signal aspect from through back contact 33, lamp R, to Hence with the train occupying the signal 6 block controlling the signal 2, such signal will display a red aspect.

As the train passes into section T3 still within the same signal block, it also shunts the track relay 3TR which drops its front contact 51 to assure that the line circuit will remain interrupted and the home-distant line relay 2H'D will remain deener-gized, its respective back contact 33 continuing to complete the above described'circuit for displaying a red signal aspect.

It should be noted that there may be several consecutive insulated sections comprising the various signal blocks, the number being dependent upon the length of the block of track desired to be control-led. The circuit organization herein disclosed will, however, remain basically the same with only the addition or elimination of intermediate track sections.

Considering again'the elfect of the train as it passes through sections T2 and T3, it was assumed that sometime during the presence of said train in each section, it provided a shunting effect during such presence of sufficient magnitude to shunt the track relays 2TR and 3TR respectively. As it is also apparent from the drawing, the circuit for shunting the external resistance R2 from the line circuit is normally interrupted and cannot be completed under any circumstances until the track relay 4TR has been deenergized. Hence, the external resistance R21, similar to the external resistance R1, as explained above, is also effective in the line circuit. The combination of these two resistances R1 and R2 connected in the line circuit in series with the relay- 2HD prevents sufiicient current to flow from the battery source to pick up the relay- ZHD. Hence, even if during the passing of the train through either track section T2 or a portion of track section T3 as described, there are periods of momentary loss of shunt or even a permanent loss, of shunt, thereby energizing the track relays 2TR and 3TR and closing their respective front contacts 43 and 51 to complete the line circuit 2A, it is impossible for the relay ZI-I-D to pick up. Thus, the signal is effectively locked in the stop position as long as the block is occupied.

Now as the train approaches the exit end of the track section T3 which is also the exit end of the signal block, the approach relay 38R will be picked up. Generally these approach relays SR are each connected across a limiting resistor LR in series with an adjustable resistor (not shown). The adjustable resistor is providedisothat an approach relay SR may be adjusted to respond to proper values of potential drop across a limiting resistor LR dependent upon the actualcircumstances of practice; but after once adjusted, it does not have a functional significance in the operation of a circuit. Thus, the slight difference interrail potential which occurs as a train approaches the source of track energy is used to energize the SR relays.

With the relay 38R picked up, front contact 14 of relay 55R in the energizing circuit for the restoration relay 3RC, is closed, energizing relay 3RC through a circuit from through front contact 14 of relay 33R, winds ings of relay SRC, front contact 35 of the home-distant line relay ll-ID, to It should be noted that the restoration circuit, by including a front contact of the HD relayof the next block in advance, thereby assures that restoration is dependent upon car movement out of the block and not upon loss of shunt while the car is still in the last track section.

If a situation should occur during the passing of a train through section T3 when the train shunt is inefieca tive to hold the track relay. 3TR down and the variation in interrail potential is insufiicient to energize the relay 38R, the restoration relay cannot be picked up. and the net [result is that the signal 2 will be locked ina stop position, indicating a malfunction of the circuit organiza: tion and requiring corrective action to be taken which would probably mean a readjustment of the variable re-i sistances associated with the relay SSR to make it more sensitive. In any event, the system operates wholly on the usual fail-safe principle desirable in all signaling systems.

Thus once the restoration relay 3RC is picked up, it closes its front contact 24 to form a stick circuit organization excluding the front contact 35 of the line relay 4HD, the energizing circuit now completed from through front contact 14 of relay 35R, winding of relay 3R0, front contact 24 of relay 3R0, to This permits the restoration relay 3RC to remain energized as the train moves into the next track section T4 and subsequently shunting the track relay 4TR, which in turn drops front contact 45 of relay 4TR, interrupting the line circuit 4A, deenergizing the line relay 4HD and consequently causing the release of front contact 35 of relay 4HD.

The shunting of the track relay 4TR also closes its back contact 44 partially completing the shunt circuit around the line circuit resistance R2. Front contact 25 of the restoration relay 3RC is also closed during this time, to also partially complete the shunting circuit. However, until relay 38R is dropped away upon complete exit of the train from the track section 3T, back contact 15 of relay 38R remains open, preventing the external resistance R2 from being shunted out of the line circuit 2A. Once the train does vacate track section 3T, the relay 3SR drops away, interrupting the energizing circuit for the restoration relay 3RC and dropping away of front contact 14 of relay 3SR. But the dropping away of relay 3'SR also closes its back contact 15 and completes the shunting circuit around the line circuit resistance R2, since back contact 44 of relay 4TR is closed upon effective shunting of track relay 4TR and front contact of relay 3RC is still closed despite the interrupting of the energizing circuit for the relay 3RC since the restoration relay 3RC has inherent slow release characteristics. It is essential, however, that the shunting circuit around the resistance R2 be completed during the established release time of the restoration relay 3RC to thereby restore the line relay 2HD in a manner described below.

If, however, the shunting circuit is not completed during the release time of the restoration relay 3RC, then a signal locked at stop will be left behind. Although subsequent trains will correct this condition, it may cause undue delay and unnecessary stops. Thus, an emergency push button control EPB has been provided by means of which restoration may be accomplished immediately upon the occurrence of such condition. For example, if the track section T4 is already occupied and a following train has occupied section 3T, so that the track circuit conditions, in accordance with the operation as hereinbefore explained, are such that both the track relay 4TR and the line relay 4HD are deenergized and their respective contacts 44 and 35 have been dropped away by the presence of a train in section T4, and, in addition, the approach relay 3SR has been picked up closing its front contact 14 and opening its back contact 15, due to the presence of the following train in section T3, then if signal 4 is a permissive stop signal and the following train chooses to exercise its option and proceed, automatic restoration is not possible. Thus, the next train through the section will be unnecessarily stopped. Hence, the engineer on the following train can stop and actuate the emergency push button control EPB thereby energizing the restoration relay 3RC. The restoration relay 3R0 will then remain picked up by virtue of the stick circuit through contact 24 of relay 3RC as described above, and its front contact 25 will again partially complete the shunting circuit around the line circuit resistance R2 also described above. Hence, when the following train vacates section T3, the dropping of the relay 38R will close its back contact 15 to complete said shunting circuit for the external resistance R2 and a restoration circuit will be completed for the relay ZHD.

The home-disant line relay 2I-ID, upon restoration as described above, will be energized over the line circuit 2A from (B),' through back contact 36 'of the line relay 4HD, back contact 44 of track relay 4TR, front contact 25 of the restoration relay 3RC, back contact 15 of relay 38R, front contact 51 of the track relay 3TR, front contact 43 of track relay 2TR, external resistance R1, windings of relay 21-11), to Since all the line relays HD are of the retained neutral polar type, this energizing current, being of reverse polarity, will actuate the polar contact 34 of relay 2HD to its left-hand position, at the same time picking up front contact 33 of relay 2HD to energize the signal circuit from through front contact 33 of relay 2HD, polar contact 34 of relay ZHD in its left-hand position, lamp Y, to Hence, with the next signal block in advance occupied, signal 2 will display a yellow aspect designating caution.

Note that the shunting circuit around the line circuit resistance R2 is completed only momentarily, contingent upon the release time of the restoration relay 3RC. Thus, the resistance R2 is shunted from the line circuit 2A only long enough to permit the line relay 2HD to be energized, then the shunting circuit is interrupted leaving the resistance R2 once against effective. But, when relay ZHD does pick up, it closes its front contact 32 which, as explained before, shunted the line circuit resistance R1 from the line sothat when line circuit resistance R2 is once again effective, line circuit resistance R1 is shunted whereby suflicient energy will continue to be supplied to line relay 2HD to maintain it in the energized position as long as the signal block is not occupied. Such energizing circuit is thus completed from (B), through contact 36 of relay 4HD, external resistance R2, front contact 51 of relay 3TR, front contact 43 of relay 2TR, front contact 32 of relay 2HD, windings of relay ZHD, to (C).

Of course when the block governed by signal 4 is vacated by the passing of the train into the next block in advance, the subsequent picking up of the line relay 4HD will pole change the front contact 36 of relay 4DH, thus reversing the polarity of the current over the line circuit 2A. Such reversal will cause the polar contact 34 of relay 2HD to move to its right-hand position, once again energizing the lamp G, and the signal 2 will display a green aspect or clear signal, all in a manner described hereinbefore.

Aside from the features pointed out in the invention described so far, the block signaling system disclosed herein has an additional advantage over the usual track circuit organization in that there is a repeated testing of the shunting performance of each track circuit under the actual existing conditions of train shunt resistance, ballast resistance, and the like. Since each car or train as it passes into a block must drop a track relay within a limited restoration time, in order to clear a stop signal behind, the failure of a track circuit to pass such auto matic testing operation is manifested by holding said signal to stop which forces adoption of corrective measures. Such advantage effectively minimizes the chance of collision when shunting failures do occur and apprises the railroads of questionable operation so that better maintenance on track circuits and equipment will neces sarily follow.

Having thus described one embodiment to which the present invention is applicable it is desired to be understood that this form was selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and it is to be further understood that various modifications, adaptations, and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What I claim is:

1. A signaling system for railroads having a stretch of track divided into a plurality of blocks, a line circuit for each block extending throughout the length of that block, a source of energy at the leaving end of each block, means for connecting each said source of energy into its line circuit for the corresponding block for normally energizing such line circuit, a line relay at the entering end of each block, stick circuit means including a stick circuit controlled by said line relay for connecting each said line relay into its said line circuit for the corresponding block, detection means for each block for deenergizing said line circuit when that block is occupied by a train, and restoring circuit means for restoring said line circuit for any block to a normally energized condition when a train in such block has fully entered the next block in advance.

2. A combination according to claim 1 wherein said 10 stick circuit means for a line relay includes a front contact on that line relay.

3. A combination according to claim 1 wherein said restoring circuit means for each block comprises a resistor for shunting said stick circuit means, said resistor having a resistance value proper to sustain its line relay picked up but failing to allow its line relay to be picked up under normal current values, and other means for causing a temporary increase in the current flow in said line circuit when a train in its block fully enters the next block in advance.

References Cited in the file of this patent UNITED STATES PATENTS 2,115,459 Gilbert Apr. 26, 1938 2,285,881 Allison June 9, 1942 2,370,620 Dower Mar. 6, 1945 2,572,234 Young Oct. 23, 1951 

